The invention relates to a circuit for the protection of consumers against damages caused by polarity reversal in a vehicle electrical system, which circuit comprises a limiter and a tripping device.
The use of specific components in motor vehicle electrical systems, particularly electrolytic capacitors or semiconductor power switches on MOSFET basis, is limited by the danger of polarity reversal. With an electrolytic capacitor, a polarity reversal can lead to the explosive destruction of the capacitor with the corresponding sequential damages. With semiconductor switches, on the other hand, a polarity reversal can lead to a high current flow over the backward diode for the standard MOS transistors, which can lead to the destruction of the switches and/or to an undesirable activation of consumers. Particularly critical are bridge circuits.
Electrolytic capacitors as well as semiconductor elements are increasingly used in motor vehicle electrical systems. Semiconductor switches are required in particular for electric motors controlled with pulse-width modulation because of the high switching frequencies. Electrolytic capacitors are used to avoid reactive effects on the vehicle electrical system.
The known option of mechanically protecting batteries in an electrical system against polarity reversal cannot be realized in motor vehicles since commercially available batteries are not suitable for this. It is not possible to protect against polarity reversal during a jump-start. Furthermore known is the practice of using seriesconnected diodes to protect individual components or individual modules against damages caused by polarity reversal. The disadvantage in that case is that with higher currents, the dissipation loss of the protective diodes increases sharply. Additional measures with lower dissipation loss involve connecting the elements to be protected in series with inversely switched MOSFETs, e.g., as known from German Patent 39 30 896. However, this solution is very expensive.
German Unexamined Published Patent Application 29 19 022 discloses using a centrally switched relay to prevent polarity reversal. However, the relay needs a relatively high tripping capacity in the switched-on state and also has a relatively high on-resistance, so that in case of a start, a worsening of the system characteristics must be expected. In addition, the shutdown of the relay in the presence of high currents involves the danger of the switching contact being welded together.
A circuit for protecting consumers against polarity reversal damages in a vehicle electrical system is furthermore known from patent GB-A-1 116 941, wherein a limiter is connected parallel to the vehicle electrical system and limits the electrical system voltage to a predetermined value in case of an incorrect polarization. The limiter is formed by a diode with a non-linear current/voltage characteristic. A separator cuts the connection to the vehicle electrical system as soon as the predetermined current value is exceeded. A standard meltdown fuse is provided as the separator. The option of actively disconnecting the vehicle electrical system, which additionally should be reversible, does not exist in this case.
A circuit is disclosed in German Patent A-195 25 112, which is designed to protect consumers against damages caused by polarity reversal in a vehicle electrical system. A limiter is connected parallel to the vehicle electrical system. In the case of polarity reversal, the limiter limits the electrical system voltage. The limiter is formed by two series-connected diodes, known per se, which have a non-linear current/voltage characteristic. An additional control circuit indirectly switches a separator that disconnects the vehicle electrical system from the consumer as soon as a predetermined current value is exceeded.
All circuits currently known from prior the art make it possible in different ways to protect the consumer against polarity reversal. All known circuits are limited to this application and have the disadvantage that they cannot be combined with additional safety devices. Additional safety devices that may be used in vehicle electrical systems must respectively be provided with complete control circuits and separators.
Thus, it is the object of the invention to provide a circuit for protecting consumers against damages from polarity reversal in a vehicle electrical system, which circuit not only can protect the consumers against damages caused by polarity reversal, but can also be combined with other protective devices and can be used as a universal protective device for various malfunction cases.